The invention pertains to devices for removing heat from an electronic component and, more particularly, to devices for transferring heat between the base and the display of a hinged mobile computing device.
Mobile computing devices such as notebook and sub-notebook computers are shrinking in size, i.e., they are becoming lighter, smaller and thinner. At the same time, the processing power of such computers continues to increase. Because the heat output of microprocessors, disk drives, power supplies and other components increases with increased processing power, challenges exist for computer manufacturers regarding dissipation of heat from notebook and sub-notebook computers. The thermal ceiling for portable computers may be approaching the saturation point. Adding large passive heatsinks and/or active cooling devices such as fan/heatsink combinations to remove heat defeats the goals of a small, light, thin computer with a long battery life. In addition, controlling temperature is also important for proper functionality, reliability and human comfort (i.e., the device cannot be unacceptably warm to the human touch).
Because the base of a hinged mobile computing device generates substantially more heat than the display unit, it is known to conduct heat from heat-generating components in the base such as a microprocessor to a heat dissipating device in the display unit. Heat is conducted via a heat pipe in thermal contact with the heat-generating component, across a thermal hinge at the location where the base is attached to the display unit, and then to a heat dissipating device via a second heat pipe. Examples of systems of the type are described in U.S. Pat. No. 5,880,929 to Bhatia, U.S. Pat. No. 5,847,925 to Progl et al. and U.S. Pat. No. 5,612,613 to Haley et al.
While such systems generally function effectively, the extent of heat transfer between base and display unit is often not as great as desired because the thermal hinge presents an undesirably large thermal resistance. Also, in some cases reliability of such systems is not as high as may desired. For example, some systems rely on the use of thermal grease for proper thermal hinge operation. This grease can dry out, escape, become contaminated with dirt, or otherwise not function as intended.
The system described in U.S. Pat. No. 5,847,925 includes heat pipes in the base and display unit which include sections that are bent so as to extend in coaxial relationship and parallel to the rotational axis of the hinges of the computing device. The ends of the heat pipes are received in a hollow tube made from a flexible, woven fabric having a relatively high thermal conductivity. The ends of the heat pipes are attached to the tube using a thermal epoxy. As the display unit is opened and closed the relative movement of the heat pipe ends is transferred to the flexible tube so as to cause the tube to be torqued along its long axis. It is believed this torquing of the flexible tube can, over time, cause reliability problems. Furthermore, the extent of heat transfer across the flexible tube is less than what is desired in some circumstances.
One aspect of the present invention is a thermal transfer hinge for transferring heat in a mobile computing device having a base, a display unit and a hinge assembly attached to the base and display unit for permitting the display unit to move between open and closed positions relative to the base, the hinge assembly having a rotational axis. The hinge comprises a first heat pipe, a second heat pipe, and first and second blocks having a thermal conductivity at least as high as copper. The first block is connected to the first heat pipe and the second is connected to the second heat pipe. The hinge also includes at least one braided metal wire attached to the first block and the second block so as to be in thermal contact with the first block and the second block. The at least one braided metal wire has a thermal conductivity at least as high as copper.
Another aspect of the present invention is a thermal transfer hinge for use in a mobile computing device as described above which includes a first heat pipe, a second heat pipe, a first block connected to the first heat pipe, and a second block connected to the second heat pipe. The hinge also includes structure for mounting the first block to the base in a first position and for mounting the second block to the display unit in a second position. In addition, the hinge has at least one braided metal wire attached to the first block and the second block so that when the first block is mounted in the first position to the base and the second block is mounted in the second position to the display unit, the at least one braided wire is caused to fold along its length around an axis extending parallel to the rotational axis of the hinge assembly when the display unit is moved between the open and closed positions.
Yet another aspect of the present invention is a mobile computing device having a thermal transfer hinge. The device comprises a base, a display unit, a hinge assembly attached to the base and the display unit for permitting the display unit to move relative to the base between an open position and a closed position, the hinge assembly having a rotational axis. The device also includes a thermal transfer hinge including a first block positioned in the base and a second block positioned in the display unit. The hinge also includes a first heat pipe positioned in the base and a second heat pipe positioned in the display unit. The first heat pipe is attached to the first block and the second heat pipe is attached to the second block. In addition, the hinge has at least one braided metal wire attached to said first block and said second block.
Still another aspect of the present invention is a method of transferring heat between a base and a display unit of a hinged mobile computing device which includes a hinge assembly attached to the base and display unit, the hinge assembly having a rotational axis. The method comprises as a first step transferring heat from a component in the base to a first portion of the base adjacent the rotational axis. Next, heat is transferred from the first portion to a second portion of the display unit adjacent the rotational axis via at least one braided metal wire having a thermal conductivity at least as high as copper. Finally, heat is transferred from the second portion to a heat-dissipating device in the display unit.